This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
Synchronous drive belts are primarily used as power transmission belts. In this use, the teeth of the synchronous drive belts engage between the teeth of an opposite belt or of a toothed disc to effect power transmission. Synchronous drive belts are often used in synchronous or positive drives, for example to provide synchronization between two or more rotating shafts.
Synchronous drive belts are frequently standard rubber toothed belts having, in general, a rearward region, a toothed front region and an interposed tensile layer based on, for example, steel or glass cord. The toothed front region frequently includes a vulcanizate based on HNBR, that is, a hydrogenated acrylonitrile-butadiene rubber copolymer, which customarily includes fillers. The mechanical and thermal resistance demands on such belts increase with increases in the power levels of the machines in which they are used. Long durability and high mechanical resistance over a broad service temperature range are therefore indispensable.
To enhance the mechanical stability of toothed belt teeth, the surfaces of the teeth may be provided with a covering, which is generally continuous and completely covers the crests, flanks and roots of the teeth. This covering can include a coating of, for example, a modified vulcanizate, or it can preferably be formed from a knitted or woven fabric. In some application, woven polyamide 6,6 stretch fabric has proved very useful for this purpose in that it has good mechanical properties and good adhesion to the tooth rubber.
In high performance synchronous drive belts a facing fabric is typically formed by viscous elastomer during the cure process, or in the case of cast polyurethane belts the layer of fabric is covered in a layer of thermoplastic polyethylene which is preformed with a heat and cool molding process, and applied to the belt mold. The facing fabric covering the toothed side of the belt helps both reinforcing the tooth, and provides a low friction wear resistant surface to engage pulleys. In use, the thermoplastic polyethylene may be prone to cold flow during service away from the loaded areas. Cold flow is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material. Cold flow is more severe in materials that are subjected to heat for long periods, and generally increases as they near their melting point.
As drive systems, such as the motor vehicles, are being equipped with more and more powerful engines or motors, and engines or motors are more and more completely enclosed to reduce noise, synchronous drive belts are exposed to ever higher operating temperatures. Thus, there exists a need for materials forming synchronous drive belts teeth which provide superior and long-term high temperature resistance and durability, such need met at least in part, with the following disclosure.